Redirect to a hash from the controller using “RedirectToAction”

I found this way:

public ActionResult MyAction(int id)
{
    return new RedirectResult(Url.Action("Index") + "#region");
}

You can also use this verbose way:

var url = UrlHelper.GenerateUrl(
    null,
    "Index",
    "DefaultController",
    null,
    null,
    "region",
    null,
    null,
    Url.RequestContext,
    false
);
return Redirect(url);

http://msdn.microsoft.com/en-us/library/ee703653.aspx